Recently, along with the explosively increasing demand for portable electric or electronic devices, the demand for secondary batteries is also rapidly increasing. In particular, lithium secondary batteries attract great attention because of their high storage capacity.
Meanwhile, as environmental problems are becoming a matter of great concern, solutions for global warming are earnestly and consistently discussed. To reduce the use of fossil fuel by vehicles, which is the main culprit of global warming, environmental-friendly electric or hybrid vehicles are becoming highly commercialized. Such electric or hybrid vehicles need large-capacity secondary batteries. Thus, a new approach to ensure the capacity and safety of secondary batteries for electric or hybrid vehicles is needed.
However, as secondary batteries tend to have larger capacities and the electrode plates of the secondary batteries have an increased unit size, the wetting capability with the electrolyte is becoming more important. While a secondary battery is produced, imperfect impregnation of the electrolyte (or imperfect wetting with the electrolyte) deteriorates capacity of the secondary battery. Additionally, the electrodes can become irregular, causing it to become a more serious matter, which makes reactions of the electrodes be concentrated to a local area. In this case, lithium metal is extruded at the local area, which may cause serious problems in relation to the safety of the secondary battery. Moreover, if the electrode plate has an increased size, the time taken for wetting the electrolyte is relatively increased, which deteriorates productivity of secondary batteries. Also, inferior wetting with the electrolyte accelerates degradation of the secondary batteries, resulting in a shortened life span of the secondary battery though other states of the battery are excellent.